Soft-sheath, stiff-core microfiber hydrogel for coating vascular implants

Vascular implants remain clinically challenged due to often-occurring thrombosis and stenosis. Critical to addressing these complications is the design of implant material surfaces to inhibit the activities of platelets, smooth muscle cells (SMCs) and inflammatory cells. Recent mechanobiology studies accentuate the significance of material elasticity to cells and tissues. We thus developed and characterized an implant coating composed of hybrid, viscoelastic microfibers with coaxial core-sheath nanostructure. The coating over metallic stent material was formed by first depositing coaxially-electrospun fibers of poly(L-lactic acid) core and polyethylene glycol dimethacrylate sheath, and then polymerizing fibers with various UV times. Material characterizations were performed to evaluate the coating structure, mechanical property and biocompatibility. Results showed that coaxial microfibers exhibited arterial-like mechanics. The soft surface, high water content and swelling ratio of the coaxial fibers resemble hydrogels, while they are mechanically strong with an elastic modulus of 172-729 kPa. The coating strength and surface elasticity were tunable with the photopolymerization time. Further, the elastic fibers, as conformal coating on stent metal, strongly reduced SMC overgrowth and discouraged platelet adhesion and activation, compared to bare metals. Importantly, after 7-day subcutaneous implantation, coaxial fiber-coated implants showed more favorable in vivo responses with reduced tissue encapsulation, compared to bare stent metals or those coated with a two-layered fiber mixture composed of fibers from individual polymers. The excellent biocompatibility aroused from nanostructural interfaces of hybrid fibers offering hydrated, soft, nonfouling microenvironments. Such integrated fiber system may allow creation of advanced vascular implants that possess physico-mechanical properties of native arteries.

TU-E-BRA-06: Evaluation of a New MV X-Ray Detector Designed for the TomoTherapy® System

PURPOSE

To evaluate the performance of a new MV X-ray detector prototype specifically designed for use on the TomoTherapy® System.

METHODS

A gas-filled detector array, similar in concept to existing TomoTherapy detector arrays, has been designed and fabricated for the TomoTherapy System. Unlike existing detector arrays, the prototype detector array has a radius of curvature that matches the source-to-detector distance. Also, the internal structure of the detector such as the septa material and geometry has been optimized for MV X-rays. The prototype detector performance was assessed by measuring the signal properties of each of the detector channel signals. Signal, noise, and signal-to-noise ratios (SNR) were measured. Finally, the resulting MVCT image quality was assessed.

RESULTS

The signal profile across the prototype detector more closely matches the incident X-ray beam intensity and, in particular, is missing the characteristic trough in the center of signal profiles from existing TomoTherapy detector arrays. Compared to an existing detector, the mean signal is approximately equal outside the central region. Inside the 100 central channels (out of 576 total channels), the prototype detector signal is substantially larger than the existing detector. The variation in the pulse-to-pulse signal (noise), after accounting for output fluctuations, is substantially lower with the new detector. The resulting SNR is an average of 18% higher across all channels, with an improvement of up to 36% for the central channels. The prototype detector yielded MVCT images that, compared to one typical system with an existing detector array, had 7% lower image noise in the periphery and 36% lower noise at the center of the image.

CONCLUSIONS

This evaluation indicates that the performance of a new MV X-ray detector array prototype exceeds the performance of an existing detector array in terms of signal-to-noise ratio and resulting MVCT image quality.

Research productivity in the areas of child abuse and domestic violence

Research productivity in the areas of child abuse and domestic violence was reviewed for the years 1990-1996 by examining articles published in Child Abuse and Neglect, the Journal of Family Violence, and the Journal of Interpersonal Violence. To examine productivity across institutions, quantification of productivity was based on ordinal position of authorship as previously used. Productivity across these three journals was also summed based on the 1987 composite productivity index formula of Howard, et al., and the data were compared with a productivity assessment based on a search process in the PsycLIT database. Rank-order correlations between the raw productivity total, the composite measure, and productivity based on first-authored publications in PsycLIT were all significant. The findings suggest that the composite measure represents a good estimate of productivity across the three journals and that publication in these three journals provides a good representation of research in the general areas of child abuse and domestic and interpersonal violence. The findings, along with implications regarding the relative utility of such information for selection of graduate programs that have a strong research focus on child abuse or domestic violence, are discussed.